Electric machines have been applied as motors and generators in a wide range of industries. A reluctance machine is an electric machine in which torque is produced by the tendency of the movable part of the machine to move into a position where the inductance of an excited winding is maximized. A switched reluctance machine is a type of a reluctance machine where the windings are energized as a function of the position of the movable part of the machine.
A switched reluctance machine is a brushless machine with salient pole construction on its rotor and stator. Conventional switched reluctance machines typically have concentrated windings around each stator pole to generate electromagnetic field. Typically, in a three-phase switched reluctance machine, depending on the number of poles in each phase, the windings around the stator poles are connected in series or parallel to create phase windings.
When a phase is energized, the flux generated by the coil windings closes its path through the rotor and the closest rotor pole rotates to get in alignment with the stator pole. Due to double saliency, i.e. salient poles on both the stator and the rotor, when the rotor pole moves towards the stator pole, the airgap length, and, hence, the stored energy changes.
The change in the stored energy depends both on the rotor position and the excitation current, and may result in a variable inductance profile, and accordingly, a pulsating torque profile.
Furthermore, since there is no excitation source on the rotor of the conventional switched reluctance machine, the radial forces acting on the rotor pole to pull it towards the stator pole causes torque ripples, vibration and acoustic noise. This also contributes to lower power density in conventional switched reluctance machines as compared to high-performance electric machines.